Tractor going into free wheel on decline

[Cassie 8]

I have 1991 Toro Wheehorse 520h which will free wheel on decline

Any suggestions how to fix this problem!

[pfrederi 17,147]

Most hydros will speed up a bit going down hill.  if yours speeds up a lot that could be from excess wear but I would think that would affect uphill performance also.  Check and make sure your hubs are not slipping on the axles.  Make a mark across the axle eds and the hub see if there is movement after a test run.

Edited February 1, 2023 by pfrederi

[lynnmor 6,774]

I have a place where my lawn suddenly goes from level to a significant downhill, the 520H speeds up till all the slack in the transmission is taken up, then it drags the tires enough to tear up the sod if it is soft.

[Handy Don 10,594]

Important to remember here is that the WH engine is NOT locked to the hydro, it uses a belt with a spring-loaded idler/tensioner

 

In the drive train, the drive belt idler is engineered to keep the belt from slipping when the engine is driving the tractor.

If the tractor is driving the engine on a downhill (steep hill or a loaded trailer?) the tension on the belt can reverse, pulling against the idler spring loosening the belt. When that happens, the belt can slip on the transaxle pulley allowing the tractor to go faster. I notice this on the steepest slope or when pulling (?) a trailer downhill with both hydros and 8-speeds.

 

That said, my experience is closer to @lynnmor’s--I get some speedup and then “engine braking.”  One thing NOT to try is moving the motion control to neutral or reverse or stomping on the brake (the brake puts the motion control to neutral and the brake alone may not be enough to stop the tractor).

 

[Ed Kennell 35,765]

1 hour ago, pfrederi said:

Most hydros will speed up a bit going down hill.

They sure do.     Another feature I like about my foot controlled hydros.      I am always controlling the speed with my foot and I simply  reduce my speed before going downhill.

[953 nut 51,655]

1 hour ago, Ed Kennell said:

 reduce my speed before going downhill

        It helps to be a bit smarter than the machine you are on. If you can use an alternate route going down hill that is not so steep you will be much safer. If this can't be done then come to a stop at the top of the steep slope and give the motion control just a slight forward touch, gravity will do the rest. Don't be in a rush.

The brakes are not on the wheels, they are on the transmission and with an open differential the tire with the least traction will stop while the other one continues to rotate. When the stopped tire gains traction it can pull your tractor in that direction and become an exciting ride

Edited February 2, 2023 by 953 nut
fat finger

[Pullstart 59,687]

I say drive fast and take chances.  See you in the Bumps and Bruises threads!  

[Ed Kennell 35,765]

6 hours ago, Handy Don said:

When that happens, the belt can slip on the transaxle pulley allowing the tractor to go faster.

I understand the  belt tension pulley is on the normally slack side of the belt,  but given the strength of the tension spring and the degree of wrap on the engine and transmission pulleys, I find it difficult to believe belt slippage is a factor in this speed increase as it usually occures just as you crest a slope and start downhill when the push from the weight of the tractor is very slight.    After the initial speed increase and the tractor is on a steeper downhill slope, the belt does not slip.  It is usually a wheel that will lose traction and slide as it will do when pulling up the same steep slope.

I don't have any data to prove the belt does not slip, but I believe the speed up is a due to a change in the hydraulic pressures inside the transmissions and any slop in the differential/axle drive gearing.          

                                                                                      

 

[TJ5208 1,823]

16 hours ago, 953 nut said:

        It helps to be a bit smarter than the machine you are on. If you can use an alternate route going down hill that is not so steep you will be much safer. If this can't be done then come to a stop at the top of the steep slope and give the motion control just a slight forward touch, gravity will do the rest. Don't be in a rush.

The brakes are not on the wheels, they are on the transmission and with an open differential the tire with the least traction will stop while the other one continues to rotate. When the stopped tire gains traction it can pull your tractor in that direction and become an exciting ride

My 520-8 locks both tires up.

[Handy Don 10,594]

12 hours ago, Ed Kennell said:

I understand the  belt tension pulley is on the normally slack side of the belt,  but given the strength of the tension spring and the degree of wrap on the engine and transmission pulleys, I find it difficult to believe belt slippage is a factor in this speed increase as it usually occures just as you crest a slope and start downhill when the push from the weight of the tractor is very slight.    After the initial speed increase and the tractor is on a steeper downhill slope, the belt does not slip.  It is usually a wheel that will lose traction and slide as it will do when pulling up the same steep slope.

I don't have any data to prove the belt does not slip, but I believe the speed up is a due to a change in the hydraulic pressures inside the transmissions and any slop in the differential/axle drive gearing.                                                       

I don’t have any actual data to support the belt slip either but I have experienced it with both 3- and 8-speed tractors and extrapolated to the possibility of it affecting hydros as well. That said, I just don’t see that any gear lash or slop between the hydro motor and the rear axle could be significant. If it isn’t belt slip, then I’d be more inclined to believe that it’s “fluid slip” via the internal acceleration valves. These are what permits the tractor to be pushed (slowly, per WH recommendations) while the engine is stopped. We all know that attempting to move the tractor quickly can damage the hydro.

 

From the Eaton 11 Service Manual:

"Internal acceleration valves are used in both forward and reverse directions. These valves are spring loaded to close "slowly”as pressure (load) increases. These valves control rate of acceleration of motor output shaft, assist in providing a positive neutral, and permit hand pushing tractor without operating engine.” (Italics added by me)

 

The “slowly” closing would correspond to the observed experience of the tractor being “pushed” downhill where it “speeds up till all the slack in the transmission is taken up, then it drags the tires enough to tear up the sod” per @Ed Kennell.  Except the “slack” is the time it takes for the acceleration valves to detect the change in pressure and react by “slowly" closing.

Edited February 2, 2023 by Handy Don

[Ed Kennell 35,765]

9 minutes ago, Handy Don said:

Except the “slack” is the time it takes for the acceleration valves to detect the change in pressure and react by “slowly" closing.

Thanks for this info Don.     This is exactly what it feels like is happening with the four Eaton 1100s that I use.

 

21 hours ago, Cassie said:

I have 1991 Toro Wheehorse 520h which will free wheel on decline

Any suggestions how to fix this problem!

 

So the answer for @Cassie is  no, there is nothing you can do to fix the problem.    Just be aware and slow down  before decending a slope.

[Handy Don 10,594]

5 minutes ago, Ed Kennell said:

So the answer for @Cassie is  no, there is nothing you can do to fix the problem

I'd phrase it as “It’s not a problem, it’s a feature. Learn to work with it!” 

[Ed Kennell 35,765]

1 minute ago, Handy Don said:

it’s a feature

Guess we can add this to the other quirky feature of the 1100s.     Some work instantly on start up and some require the recommended 10 minute warm up.

[Ed Kennell 35,765]

Downhill speed increase isn't limited to our tractors.

While driving Mrs. Ks Dodge Caravan yesterday, I noted a speed increase as I crested a hill.  It has a 4 speed hydro tranny and can be manually downshifted to help control the speed which I do all the time.

My F-150 has an automatic jake break tow/ haul gear that will use the engine to control downhill speed.

[kpinnc 10,715]

There was some discussion several years back about this, and some felt that the freewheeling was an indication of the hydro beginning to fail. My 520-H has done it for 10 years, and it's still the fastest Eaton hydro I have. It will spin the tires on my gravel driveway even after running an hour in the summertime.

 

I had another 520-H that did have a "weakening" hydro. It was a completely different indication. That tractor would skip and surge, and it got increasingly worse as it warmed up- to the point it would barely move while climbing a slight grade. 

 

It may be that freewheeling is an indication of a valve spring getting weaker, but I don't think it's indicative of a worn tranny at all. 

[NA73 66]

think about it... when there is no load on a hydraulic cylinder it moves faster than if there is 'max load'.

same thing with the transmission. 'up-hill' makes an increased load - additional force/pressure required.

down-hill is a 'no load' or even 'negative load' situation which lets the oil flow freely and motor spin at whatever is

[Handy Don 10,594]

I’d hate to generalize much detailed connection between the Eaton 11 and any automotive transmission. One of my vehicles specifically calls out that the transmission will allow the car to “coast” on downhills up to a certain speed to save fuel. However, it then it locks up the transmission to slow the car via engine braking, i.e. it uses the same “lock up” that makes the transmission efficient in normal driving.

An unworn Eaton has relatively little fluid bypass leakage. Absent its acceleration valves, it would be a near-direct lockup from pump to motor given that the fluid is incompressible (there are a couple of small damper pistons but their effect is momentary and quickly transient). Note that Sundstrand piston hydros don’t have the same sort of built-in acceleration valves and need the manually activated bypass valve to permit rolling the tractor without the engine running. They also probably hold back nicely on downhils!

 

So back to those valves...

Here’s a patent describing the way they work. Generally, it is a controlled fluid bypass of the hydro motor.

When normal motion control goes from neutral to forward, say, the pump is outrunning the hydro motor so the “forward" valve opens to smooth the acceleration and discourage burning rubber or popping wheelies.

But when the tractor is being pushed with the engine off or is going faster than the engine on a downhill, the hydro motor is outrunning the pump and so the pressure difference causes fluid to flow through the open “reverse" valve until it detects the pressure/flow and reacts (slowly, by design) and closes.

So the same system that “smooths” acceleration, “smooths” the transition from freewheeling to under control.

 

All that said, IMHO with closed acceleration valves, the hydro might still cause belt slip on downhills despite the substantial belt wrap at the engine and pump pulleys.

 

Edited February 4, 2023 by Handy Don